Run browser tests in parallel shards with 4 workers

.github/workflows/quality.yml

@@ -88,10 +88,27 @@ jobs:
       - name: Check patch hygiene
         run: git diff --check
 
-  browser:
+  browser-shard:
+    name: browser (${{ matrix.project }})
     needs: validate
     runs-on: ubuntu-latest
     timeout-minutes: 35
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - project: chromium
+            engine: chromium
+          - project: chromium-dark
+            engine: chromium
+          - project: mobile-chromium
+            engine: chromium
+          - project: firefox
+            engine: firefox
+          - project: webkit
+            engine: webkit
+          - project: mobile-webkit
+            engine: webkit
 
     steps:
       - name: Checkout repository
@@ -114,13 +131,25 @@ jobs:
         run: |
           python -m pip install -r requirements-docs.txt
           npm ci
-          npx playwright install --with-deps chromium firefox webkit
+          npx playwright install --with-deps ${{ matrix.engine }}
 
       - name: Build site
         run: npm run docs:build
 
       - name: Run critical journeys and accessibility checks
-        run: npm run test:browser
+        run: npm run test:browser -- --project=${{ matrix.project }}
+
+  # Branch protection requires a check named "browser"; this job passes only
+  # when every browser shard above passed.
+  browser:
+    needs: browser-shard
+    if: always()
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+
+    steps:
+      - name: Require every browser shard to pass
+        run: test "${{ needs.browser-shard.result }}" = "success"
 
   lighthouse:
     needs: validate

playwright.config.mjs

@@ -9,7 +9,7 @@ export default defineConfig({
   fullyParallel: true,
   forbidOnly: Boolean(process.env.CI),
   retries: process.env.CI ? 2 : 0,
-  workers: 2,
+  workers: process.env.CI ? 4 : 2,
   timeout: 30_000,
   expect: {
     timeout: 8_000